ABSTRACT
Lysine acetylation has emerged as one of the most important post-translational modifications that participates in various biological and pathological processes. Histone acetyltransferase 1 (HAT1) as the first identified protein ε-amino lysine acetyltransferase is able to regulate the acetylation of histones and non-histone proteins. However‚ the acetylation substrates and sites mediated by HAT1 in liver cancer are poorly understood. In this study‚ we demonstrated that HAT1 was highly expressed in the liver cancer tissues‚ which was negatively associated with the prognosis of patients. Based on the establishment of the HAT1-knockout HepG2 cell line‚ we employed a quantitative proteomics approach to study the profiling of acetylation mediated by HAT1 in HepG2 cells. Interestingly‚ we identified a total of 858 Kac sites on 547 proteins in the HepG2 cell line‚ in which HAT1 mediated the levels of Kac of 74 sites on 68 proteins. The pathways and metabolic processes that were affected by HAT1-dependent acetylation modification were analyzed by bioinformatics. The results show that Kac regulates disease development‚ RNA biology‚ spliceosome and nucleosome assembly‚ oxidative stress‚ various signaling pathways and metabolic pathways‚ etc.. Moreover‚ we verified that the HAT1-mediated acetylation modification could promote abnormal lipid metabolism. CCK8 assays‚ clone formation and Edu assays revealed that HAT1 could remarkably enhance the cell proliferation of liver cancer in vitro. Thus‚ our finding explored the profiling of HAT1-mediated protein acetylation in HepG2 cells‚ which provides new insights into the underlying mechanism by which HAT1 mediates the development of liver cancer. Clinically‚ the HAT1-mediated acetylation sites could be used for the precise targets of drug development.
ABSTRACT
Polyamines regulate gene expression in Escherichia coli by translationally stimulating mRNAs encoding global transcription factors. In this study, we focused on histone acetylation, one of the mechanisms of epigenetic regulation of gene expression, to attempt to clarify the role of polyamines in the regulation of gene expression in eukaryotes. We found that activities of histone acetyltransferases in both the nucleus and cytoplasm decreased significantly in polyamine-reduced mouse mammary carcinoma FM3A cells. Although protein levels of histones H3 and H4 did not change in control and polyamine-reduced cells, acetylation of histones H3 and H4 was greatly decreased in the polyamine-reduced cells. Next, we used control and polyamine-reduced cells to identify histone acetyltransferases whose synthesis is stimulated by polyamines. We found that polyamines stimulate the translation of histone acetyltransferases GCN5 and HAT1. Accordingly, GCN5- and HAT1-catalyzed acetylation of specific lysine residues on histones H3 and H4 was stimulated by polyamines. Consistent with these findings, transcription of genes required for cell proliferation was enhanced by polyamines. These results indicate that polyamines regulate gene expression by enhancing the expression of the histone acetyltransferases GCN5 and HAT1 at the level of translation. Mechanistically, polyamines enhanced the interaction of microRNA-7648-5p (miR-7648-5p) with the 5'-UTR of GCN5 mRNA, resulting in stimulation of translation due to the destabilization of the double-stranded RNA (dsRNA) between the 5'-UTR and the ORF of GCN5 mRNA. Because HAT1 mRNA has a short 5'-UTR, polyamines may enhance initiation complex formation directly on this mRNA.
